Source files (.h files)
Every function (and external variable) must be defined exactly once by giving a full definition in some .c source file.
A function (or external variable) may be called (or referenced) in other files provided that there is a declaration of the function (or external variable) in the other files.
The declaration of a function gives the function name and parameters, but not the function body. Example: int max(int x, int y);
Related declarations are often grouped in header files (name ending in �.h�). The declarations in a head file xyz.h can be incorporated in another file by the directive
- #include �xyz.h� (for user files)
or
- #include <xyz.h.> (for standard C libraries)